Compression release engine braking is typically used in trucks, buses and other heavy machines. Compression release engine brake systems typically operate by opening a valve, such as an exhaust valve associated with an engine cylinder near the top dead center position of a corresponding piston during a compression stroke. Thus, the work performed by the engine to compress the air in the cylinder is dissipated before the piston moves away from the top dead center position.
Compression release engine braking is typically activated if certain engine and machine operational conditions are met. Such conditions may include clutch status, transmission status, engine speed, or whether the engine is in positive power mode (i.e., whether fuel is being supplied to the engine).
Most compression release engine braking systems and methods designate a predetermined minimum engine speed for braking, below which compression release engine braking will not be enabled. In such systems, compression release engine braking will disable when engine speed falls below the predetermined speed limit. For example, U.S. Pat. No. 5,967,115 discloses a compression release braking system that disables if the engine speed falls below a level that is fixed and predetermined for all engine operating conditions. In such systems, however, the minimum engine speed limit for braking is predetermined and cannot vary continuously based on the operational parameters of the machine. Accordingly, the minimum engine speed limit for braking may not represent the true minimum engine speed limit for braking under certain operational conditions. The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.